According to the wiki of the dream argument, "the act of dreaming provides preliminary evidence that the senses we trust to distinguish reality from illusion should not be fully trusted, and therefore, any state that is dependent on our senses should at the very least be carefully examined and rigorously tested to determine whether it is in fact reality."

When reading this, I can't help but wonder why dreaming is considered a product of the senses. Would dreaming not be a product of the mind instead of the senses? If so, then why is it the senses that are being distrusted? Is it because the senses provide us with an account of an external reality that the mind is able to generate from within?

Moreover, in the simulated reality section of the wiki, the justification is as follows: it is possible for "the mind to be tricked into believing a mentally generated world is the 'real world.'"

This too makes me wonder why the senses are being distrusted if it's the mind that is being tricked. Why should we trust something that can be tricked in the first place?

When reading René Descartes' First Meditation (first paragraph on page 7), it becomes clear that he did distrust the mind along with the senses, since he asked: "how do I know that I am not deceived every time that I add two and three [in the mind], or count the sides of a square [in the mind], or judge of things yet simpler, if anything simpler can be imagined [by the mind]?"

I've been looking for articles that seriously question the trustworthiness of the mind, but the only ones I could find were those unsatisfactory "10 ways the mind deceives you" clickbait articles, and so it appears that the mind is generally trusted for no good reason other than necessity. I mention necessity because, after having pondered on this the entire day, the only valid reason I arrived at is that the mind is trusted simply because nothing remains to be trusted if the mind is distrusted (because everything is processed by the mind).

All this deep contemplation made me wonder whether there are any instances that prove that the mind can deceive itself in situations where sensory information is not a factor, such as through internal logic, arithmetic, or geometry. However, I could not come up with any valid argument against the mind, and now I wonder whether this proves that the mind is trustworthy on its own, although that is a fallacy since absence of evidence is not evidence of absence (if an argument can be imagined by you, please share it since it would contribute significantly to this question!).

I get that the senses may be providing the information that ultimately tricks the mind (i.e., the senses do the tricking), but that still does not explain why only the senses are considered to be untrustworthy. I'm looking for an answer as to why the mind is considered trustworthy, or an answer that contains an argument that indicates that the mind is not trustworthy either.

  • When people say the senses are untrustworthy they will usually mean that sensory information is 'theory-laden'. That is, it is not received as raw data but only after some processing. This introduces the possibility of error. I expect most people would be happy to concede it is the mind that introduces this error, not the senses themselves, since the error is not in the raw data.
    – user20253
    Commented Jul 15, 2018 at 12:41
  • "Senses" is just a shorthand, there is much mental processing involved even in the ordinary perception beyond pure "sense data" (such a "pure" thing is itself idealized fiction). The ability to judge reality from illusion is obviously even more complex, and involves mental faculties way beyond perception. But there is no reliable way to separate what "senses" provide from mind's handiwork, even what we "see" already carries much of it. So there is no reason to trust what mind does to the "sense data", let alone if it can tell the difference between perception and its own productions.
    – Conifold
    Commented Jul 15, 2018 at 22:35

1 Answer 1


You have already worked out some key points for yourself. I think Descartes would say that dreaming is a state of mind and that dreams are products of the mind. He is not at this stage of the argument in the 1st Meditation wholesale sceptical of the senses - that comes later with the Evil Demon. Awake, when I look out of the window I might really see a tree (my example) but, dreaming, I might imagine that I am looking out of the window and seeing a tree. The problem is that I do not know whether I am awake or dreaming. When I am awake I think I am awake and when I am dreaming I also think I am awake. To borrow from Bernard Williams' statement of Descartes view: if when I am dreaming I don't know that I am, when I am not dreaming I don't know that I am not.

There is something deeply wrong about the argument of the 1st Meditation. Not only does Descartes, at least for a large part of the argument, assume the veracity of memory; more than that, for all the power he hypothetically ascribes to the Evil Demon, in particular that the Demon can cause him falsely to believe in the truth of mathematics and the validity of deduction, Descartes uses deductive argument throughout. He uses deduction to 'prove' that the Demon can deceive him about the validity of deduction, and it is his continued use of deduction that lands him in the final predicament of the 1st Meditation - that of 'the inextricable darkness of the problems I have now raised' (The Philosophical Writings of Descartes, tr. J. Cottingham et al., II, Cambridge : CUP, 1984:15.

Indeed Descartes continues to rely on deductive reasoning in the 2nd Meditation in the process of delivering the Cogito. The validity of deduction is never actually put practically in doubt anywhere in the Meditations.


The questions have been put : 'Do you think that Descartes did not question the mind properly because it would undermine his deductive reasoning? Is necessity the only reason the mind is trusted?'

In effect Descartes does 'question the mind' in Meditation 2. The claim, 'I am a mind' (Cottingham, 18), follows a series of reflections in which he is (clearly) thinking and realises this, then infers that where there is thinking there is a mind. But he realises that he must not infer too much. In particular, the mind might have only a point-instant existence. Where there is thinking there is a mind, but this does not imply the existence of the same mind over time. Descartes deals with the continued existence of the same mind later : Med. 6 where he satisfies himself that his mind is a substance - a continuant. I am not entirely clear about the reference to 'necessity' in the second question - the necessity of what ? If the query is why Descartes wants so much to rely on deductive reasoning, in which the truth of the premises necessitates the truth of the conclusion, and why he thinks deductive reasoning can prove the existence of God and other ambitious things, I can only point out that Descartes belongs to a different age from ours. He believes that deduction, aided (be it added) by intuition, is the right way to proceed in philosophy and the sciences.


The Philosophical Writings of Descartes, tr. J. Cottingham et al., II, Cambridge : CUP, 1984.

Bernard Willliams : Descartes: The Project of Pure Enquiry. ISBN 10: 0140138404 / ISBN 13: 9780140138405 Published by Penguin Books Ltd, 1978/ 1990. (Many reprints.)

  • Do you think that Descartes did not question the mind properly because it would undermine his deductive reasoning? Is necessity the only reason the mind is trusted? Commented Jul 15, 2018 at 20:34
  • @user Descartes questions preconceived notions, including those of the mind, but not everything of it all at once. For instance, see Objections and Replies esp. pp. 84-85, 100 responding to Gassendi. He admits that we can't get rid of all the notions of the mind, but only "to all the present opinions that are residues of previous judgments that we have made" (85). In effect, he introduces plausible doubt about our prejudices and preconceived notions in order to fairly examine which (if any) of them are properly justified.
    – Greg S
    Commented Jul 16, 2018 at 2:57
  • @user3776022. Thank you for your questions. I have replied to them in my revised answer.
    – Geoffrey Thomas
    Commented Jul 16, 2018 at 7:57

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